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1
Dixon, Zach Adam. "The role of CREBBP mutations in lymphoid malignancies." Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3556.
Texte intégralRésumé :
Relapsed acute lymphoblastic leukaemia (ALL), diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) comprise a group of malignancies with poor prognosis and therapeutic strategies are needed to improve outcomes. Recent studies have shown that heterozygous inactivating mutations in the histone acetyl transferase, CREBBP, are frequent in these malignancies, and are thought to lead to impaired transcription of glucocorticoid (GC) response genes. Given the pivotal role of GC in the treatment of lymphoid malignancies and the finding that CREBBP mutations often arise at relapse, it has been postulated that CREBBP mutations confer chemoresistance to GC therapy. To study the role of CREBBP haploinsufficiency in ALL, DLBCL and FL, small hairpin RNA and small interfering RNA methods were used to knock down CREBBP in a number of cell lines and primary derived samples. Models were functionally relevant, with reduced acetylation of CREBBP target residue, histone 3 lysine 18 and/or histone 3 lysine 27, but knockdown had no significant impact on activation of cAMP-dependent target genes. Impaired induction of glucocorticoid receptor targets was only seen in 1 of 4 CREBBP knockdown models of ALL, and there was no significant difference in GC-induced apoptosis or chemosensitivity to other therapeutic agents frequently used in lymphoid malignancies, including histone deacetylase inhibitors. However, CREBBP knockdown was associated with enhanced signalling of the RAS/RAF/MEK/ERK pathway in RAS pathway mutant ALL cells, and MEK inhibitor sensitivity was retained. This suggests that CREBBP mutation may act to enhance the activity of oncogenes and that CREBBP/RAS pathway mutated relapsed ALL are candidates for MEK inhibitor clinical trials.
2
Dawes, Joanna Camilla. "Modelling Crebbp loss in BCL2 driven non-Hodgkin's lymphoma." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/58194.
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Non-Hodgkin’s lymphomas (NHL) are a spectrum of hematopoietic cancer accounting for 4% of new cancer diagnoses each year. Approximately 95% of all NHL are of B-cell origin; diffuse large B-cell lymphomas (DLBCL) and follicular lymphoma (FL) accounting for 30-40% and 20% of B-NHL respectively. Recent human mutation profiling and resequencing studies have shown that CREBBP and BCL2 are frequently mutated, early events in B-NHL that are often are concurrent. This thesis presents a study of their role in oncogenesis by generating a novel model of B-NHL overexpressing BCL2 in the haematopoetic compartment combined with the conditional heterozygous loss of Crebbp in the germinal centre B-cells. Loss of Crebbp significantly accelerated BCL2 driven lymphomagenesis. Characterisation of these lymphomas by flow cytometry demonstrated that they were phenotypically similar to mature human B-cell lymphomas of germinal centre origin. Additionally an insertional mutagenesis screen was performed in mice sensitised to B-NHL. Somatic MoMuLV caused mutations interact with the sensitising mutations, facilitating tumourigenesis and recapitulating the stepwise and accumulative progression of human disease. Provirus insertions were detected using a novel method of insertion site cloning called UMI-LM-PCR which amplifies the region flanking the provirus. Insertions were then mapped to the mouse genome flagging genes with a putative role in tumourigenesis. This method represents the highest throughput method to date and its applicability to Illumina sequencing permits the most comprehensive quantitative survey of subclonal mutations. This work confirms Crebbp is a tumour suppressor gene and that its loss cooperates with overexpression of BCL2 to accelerate lymphomagenesis. Through insertional mutagenesis screening of this model hundreds of putative cancer genes have been identified including Pou2f2 and Tfrc which have a propensity for mutation specifically in B-cell lymphomas deficient in Crebbp and overexpressing BCL2. These candidates now need to be validated to better characterise their role in B-cell lymphoma.
3
BENTIVEGNA, ANGELA. "Ricerca di alterazioni del Gene CREBBP (CREB Binding Protein) in pazienti con sindrome di Rubinstein-Taybi." Bachelor's thesis, Università degli Studi di Milano-Bicocca, 2004. http://hdl.handle.net/10281/12824.
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Di, Dio Laura Giusy Rosaria Agata. "Sindrome da microduplicazione 16p13.3 espansione del fenotipo." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/1062.
Texte intégralRésumé :
Le sindromi da microalterazione cromosomica sono sindromi costituzionali con ritardo mentale e anomalie fenotipiche multiple causate da sbilanci di specifiche regioni del genoma. Se il riarrangiamento cromosomico include poche megabasi viene detto criptico perché spesso non è diagnosticabile con un esame cromosomico convenzionale.
Per molti anni, tuttavia, cioè fino a quando è stata disponibile solo la tecnica tradizionale e FISH per l analisi di cromosomi metafasici, erano conosciute soltanto le microdelezioni delle regioni fiancheggiate da dupliconi. La mancata diagnosi citogenetica-molecolare delle microduplicazioni è stata attribuita a vari possibili fattori: ad un evento selettivo di microdelezione mediato dai dupliconi,
ad una mancata penetranza clinica della duplicazione, che, essendo in genere meglio tollerata sul piano fenotipico rispetto alla delezione, può sfuggire all accertamento clinico.
In realtà l applicazione della tecnica array-CGH nella diagnosi del ritardo mentale idiopatico, sta dimostrando come le stesse regioni interessate da microdelezione siano spesso interessate da microduplicazione, con possibile fenotipo clinico, confermando che il meccanismo di ricombinazione omologa non allelica è un frequente e specifico meccanismo di mutazione cromosomica strutturale.
Nel genoma sono presenti CNV (copy number variation) o polimorfismi (delezioni, duplicazioni, amplificazioni) che hanno diverse dimensioni da 40kb a 2Mb e sono ampiamente distribuiti in tutto il genoma. Vista l ampia distribuzione di CNV lo studio del DNA parentale aiuta l interpretazione dei dati forniti dagli array-CGH.
Un ulteriore tipologia della tecnica di array-CGH è quella definita SNP array (Single Nucleotide Polymorphism). Questa metodologia sfrutta l elevato polimorfismo di genomi individuali relativi a singoli nucleotidi. La tecnica SNP array è in grado di diagnosticare non solo variazioni quantitative del genoma ma anche le disomie uniparentali, l origine parentale di uno sbilancio.
Riportiamo un caso con caratteristiche fenotipiche riconoscibili, ritardo psicomotorio e di crescita, in cui è stata rilevata dagli SNP-array una duplicazione di 0.4 Mb nella regione cromosomica 16p13.3. Tale regione è implicata nella sindrome di Rubinstein Taybi, dovuta a microdelezione della regione o delezione del gene CREBBP o mutazione del gene CREBBP con loss of function.
5
BENTIVEGNA, ANGELA. "Base molecolare della sindrome di Chromatin remodelling Rubinstein-Taybi: un sistema modello per lo studio dei deficit funzionali di acetilazione istonica." Doctoral thesis, Università degli studi di Milano, 2008. http://hdl.handle.net/10281/12823.
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Rubinstein–Taybi syndrome (RSTS) is a rare malformation disorder caused by mutations in the closely related CREBBP and EP300 genes, accounting respectively for up to 60 and 3% of cases. About 10% of CREBBP mutations are whole gene deletions often extending into flanking regions. Using FISH and microsatellite analyses as a first step in the CREBBP mutation screening of 63 Italian RSTS patients (pts), 6 deletions were identified, 3 of which were in a mosaic condition that has not been previously reported in RSTS. The clinical presentation was typical in all cases, but more severe in the three pts carrying constitutional deletions, raising a question about the possible underdiagnosis of a few cases of mild RSTS. The use of region-specific BAC clones and small CREBBP probes allowed to assess the extent of all of the deletions by mapping their endpoints to genomic intervals of 5–10 kb. Four of five intragenic breakpoints cluster at the 5' end of CREBBP, where there is a peak of breakpoints underlying rearrangements in RSTS pts and tumours. The search for genomic motifs did not reveal any low-copy repeats (LCRs) or any greater density of repetitive sequences. The FISH analysis extended to the EP300 genomic region did not reveal any deletions. Searching for mutations of CREBBP gene in 56 patients revealed 23 different mutations. In addition, one deletion and two amplifications were identified by a-CGH in 20 RSTS pts.
6
Camós, Guijosa Mireia. "Caracterización biológica de la leucemia mieloide aguda con translocación t(8;16)(p11;p13) y reordenamiento MYST3-CREBBP." Doctoral thesis, Universitat de Barcelona, 2007. http://hdl.handle.net/10803/2220.
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INTRODUCCIÓN. La leucemia mieloide aguda (LMA) es una enfermedad heterogénea desde el punto de vista clínico y biológico. En los últimos años se vienen reconociendo diversas alteraciones moleculares que definen entidades específicas. En este contexto, la LMA con translocación t(8;16)(p11;p13) y reordenamiento MYST3 (MOZ)/CREBBP (CBP) es una variedad infrecuente mal caracterizada desde el punto de vista biológico. <br/><br/>HIPÓTESIS Y OBJETIVOS. La proteína quimérica MYST3-CREBBP, resultante de la translocación t(8;16)(p11;p13), podría conferir a este subtipo de LMA una individualidad biológica propia, con rasgos diferenciados respecto al resto de leucemias. Para confirmar esta hipótesis general los objetivos de la presente tesis doctoral fueron: 1) diseñar una técnica de PCR para el diagnóstico rápido y específico del reordenamiento MYST3-CREBBP; 2) caracterizar el punto de ruptura de los genes implicados en la translocación en una serie de pacientes y 3) estudiar el perfil de expresión génica de las LMA con reordenamiento MYST3-CREBBP y compararlo con el de otros subtipos bien definidos de LMA.<br/><br/>PACIENTES Y MÉTODOS. Se estudió una serie de pacientes con LMA y reordenamiento MYST3-CREBBP (n=7) y se compararon sus características biológicas con otros casos de LMA. Para ello se diseñó una técnica de PCR nueva para la detección del reordenamiento MYST3-CREBBP, mientras que los puntos de ruptura de los genes implicados en la translocación se estudiaron mediante secuenciación directa. El estudio del perfil de expresión génica de la LMA con reordenamiento MYST3-CREBBP se abordó utilizando microarrays de oligonucleótidos (Affymetrix HU133A). La diferencia entre la expresión génica entre diferentes subtipos de leucemia se analizó con diversas técnicas estadísticas (ANOVA, t-test), utilizando diferentes programas informáticos. Los resultados de este análisis se validaron en una serie independiente de pacientes estudiados mediante RT-PCR cuantitativa utilizando arrays de baja densidad. <br/><br/>RESULTADOS. Los pacientes afectos de LMA con reordenamiento MYST3-CREBBP presentaron un inmunofenotipo característico (CD34-, HLA-DR-, CD117-, CD56+, expresión de marcadores mielomonocíticos). Por otro lado, el análisis molecular reveló que el tránscrito tipo I del gen quimérico MYST3-CREBBP es el más común en estos pacientes. Por otra parte, el análisis sobre el perfil de expresión génica mostró una firma característica para las LMA con reordenamiento MYST3-CREBBP, consistente en la sobreexpresión de determinados genes HOX (HOXA9, HOXA10), de los oncogenes RET y PRL y la infraexpresión de genes como CCND2, STAT5 y WT1. Por otro lado, se observó una similitud en la expresión de algunos genes entre las leucemias MYST3-CREBBP y las LMA con reordenamiento de MLL, lo que sugiere un mecanismo de leucemogénesis parcialmente compartido por los dos tipos de leucemia.<br/><br/>CONCLUSIONES. La técnica de RT-PCR implementada es útil para la detección rápida del reordenamiento MYST3-CREBBP. El denominado tránscrito tipo I del gen quimérico MYST3-CREBBP es el más común en la LMA con t(8;16). La LMA con reordenamiento MYST3-CREBBP posee un perfil de expresión característico, con sobreexpresión de diversos oncogenes como RET y PRL y la presencia de un patrón específico de expresión de los genes homeobox.
7
Torres, Leuridan Cavalcante. "Avaliação da imunocompetência de portadores da síndrome de Rubinstein-taybi." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/42/42133/tde-01092008-192345/.
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A síndrome de Rubinstein-Taybi (RTS, OMIM 180849) é uma doença autossômica dominante caracterizada por dismorfismos craniofaciais típicos, polegares e háluces alargados, infecções respiratórias recidivantes, retardo mental e de crescimento. RTS está associada com mutação no gene CREBBP. Na avaliação da imunocompetência de 17 portadores de RTS, observaram-se algumas alterações na resposta imune inata e adaptativa: leucocitose persistente, neutrófilos com desgranulopoiese, elevada concentração sérica de IgM e IgG1, produção normal de anticorpos contra antígenos protéicos e anti-polissacarídeos, elevados valores absolutos de células B totais, B \"naive\", B de memória, subpopulação B1 e de linfócitos B com IgM de membrana, e elevado percentual de apoptose de linfócitos B. DTH negativo para três antígenos e baixa resposta linfoproliferativa para antígenos protéicos. Diante do exposto, concluímos que os pacientes RTS apresentam alterações em vários mecanismos da resposta imune e principalmente, na imunidade humoral. Portanto, com este trabalho foi possível identificar as principais alterações imunológicas destes pacientes, e com isso, caracterizar quais os defeitos da resposta imune que pode estar associada com gene CREBBP.<br>Rubinstein-Taybi syndrome (RTS, OMIM 180849) is a dominant Mendelian disorder characterized by craniofacial dysmorphisms, broad thumbs and toes, mental retardation and growth and recurrent respiratory infections. RTS is classically associated with CREBBP gene mutations, but recently, p300 gene mutations were reported in three individuals. In imunonocompetence investigation of a group of 17 patient of the RTS, we found that the patients really show alterations in more than one arm of the immune response. The main alterations were found in: a) innate immunity, patients have defects in the distribution of the granules citoplasmatic and partial absence of F-actin filament part of its polymorphonuclear cells. In addition, some patients had decreased phagocytic activity, b) humoral immunity: elevated serum IgM antibodies and IgG1 subclass, normal production of antibodies for protein antigens and antipolysaccharide, high absolute values of B cell total, B \"naive\", B memory, subpopulation B1 and B lymphocytes with the membrane IgM, and high percentage of apoptosis of B lymphocytes; c) cellular immunity: delayed hypersensitivity skin tests negative for three antigens and low lymphoproliferative response to protein antigens. Values reduced percentage of CD45RA+ , CD45RO+ T cells and high doublepositive CD45RA+/CD45RO +) T cell. Ahead of the severe recurrent respiratory infections that affect the patients with RTS, and of the evaluation of immunocompetence of these patients, we find that they have several alterations in mechanisms of immune response and mainly in humoral immunity. Therefore, with this study was to identify the major immunological alterations of these patients, and with this, which characterize the main defects of the immune response of the patients RTS that can is associated with gene CREBBP.
8
Djavanroodi, Faramarz. "Creep and creep-fracture crack growth." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47412.
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Whitt, Harrison Collin. "Creep and Creep-fatigue Deformation Studies in 22V and P91 Creep-strength EnhancedFerritic Steels." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555603135480185.
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Giannopoulos, Ioannis. "Creep and creep-rupture behaviour of Aramid fibres." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/252181.
Texte intégralRésumé :
To obtain creep-rupture data at low level within a reasonably short time-scale, two accelerated techniques have been investigated. Stepped Isothermal Method (SIM) testing involves loading a single specimen, under constant load, with the temperature increased in a series of steps to accelerate the creep. Careful choice of the temperature step and step duration allow the test to be completed in about 24 hours. At each temperature step a creep curve is obtained; these are then adjusted to compensate for the different temperature levels and a creep master curve at a reference temperature is produced. In Stepped Isostress Method (SSM) testing, a similar approach is adopted but the acceleration is obtained by increasing the stress in steps while keeping the temperature constant. Additional stress provides energy to the system in an analogue of the effect of heat in SIM. In this thesis, SIM and SSM tests have been successfully applied to two slightly different aramid fibres, Kevlar 49 and Technora, for a wide range of loads (50-80% ABL). The test data are used to determine the creep and creep-rupture behaviour of the two materials. The creep master curves obtained by accelerated testing are compared with conventional creep tests at ambient conditions, and good agreement of the data is observed. A rheological model for the prediction of the creep and creep-rupture of the two fibres is established to facilitate and greatly increase the reliability of the prediction of the long-term behaviour. This investigation allows more certainty about the creep-rupture relationships for different high modulus fibres, which will in turn allow more realistic safety factors to be applied when using these materials in engineering applications.
11
Jones, J. P. "Creep and creep fracture of alpha/beta brass." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637455.
Texte intégralRésumé :
The uniaxial creep and creep fracture properties of α/β brass in air, have been determined over the stress range 9MPa - 185MPa at 523-673 K, using high precision constant stress creep testing machines. In the majority of cases, normal creep curves were recorded however, under certain conditions, due to the interactions of the two constituent phases some curves exhibited two areas of primary creep. Traditional Power Law analysis was carried out, and was found to be in agreement with published data. An alternative approach, known as the θ Projection Concept accurately described the accumulation of strain with time. Creep fracture was found to occur as a result of the accumulation of damage, primarily at α-β interfaces. To investigate the effect of varying stress states, biaxial creep testing was carried out at an effective stress of 140MPa at 523K. Using uniaxial and multiaxial test data, the θ Projection Concept was further developed to critically evaluate the damage processes occurring and their dependence on stress state. It was found that a damage at failure parameter, ω, decreased with increasing maximum principal stress.
12
Abdallah, Zakaria. "Creep lifing methods for components under high temperature creep." Thesis, Swansea University, 2010. https://cronfa.swan.ac.uk/Record/cronfa43065.
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Hayes, Troy Allyn. "Creep and creep fracture of zirconium and zirconium alloys /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3123657.
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Thornton, Gail Marilyn. "Creep behaviour and creep mechanisms of normal and healing ligaments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0023/NQ49542.pdf.
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Pearce, I. "Creep rupture and creep life prediction of aluminium airframe alloys." Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638435.
Texte intégralRésumé :
Aluminium alloys 2419-T851, 2124-T851 and 7010-T7351 are candidates to succeed the current airframe alloy, RR58. In the present work, high precision constant stress creep curves have been obtained for alloys 2419-T851 and 7010-T7351 over an approximate stress range 100-400MPa at 373-463K. In the case of alloy 2419-T851, the creep curves recorded were predominantly primary in nature, alloy 7010-T7351 exhibited predominantly tertiary curves, while creep curves reported <SUP>(2)</SUP> for 2124-T851 showed an intermediate curve shape. These results have been analysed to allow comparisons to be made between conventional methods of creep data representation and a new approach, termed the theta Projection Concept.
16
Ward, A. R. "Creep and creep fracture of alpha + beta titanium alloy 6.2.4.6." Thesis, Swansea University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639344.
Texte intégralRésumé :
High precision uniaxial constant stress creep tests were carried out at 773K for the α+β titanium alloy Ti 6.2.4.6. Repeat data at 580 MPa provided a unique opportunity to identify stochastic creep properties and to use this information to build a probabilistic creep damage assessment for this alloy. The stochastic nature of creep properties both at a single test condition (using a generalised gamma distribution) and at various test conditions (by combining this distribution with the Monkman - Grant relation) was identified. In addition, the theta prediction methodology was extended so that life predictions for materials operating under long service conditions can be made that also have a degree of confidence associated with them. Ways in which the theta model can be applied to the fatigue as well as the creep of all materials are also discussed. For comparison purposes two failure criteria are built into the stochastic model and the determinants of failure derived. This stochastic theta model is then used to investigate the nature of the creep failure time distribution for the Ti 6.2.4.6 alloy under constant uniaxial conditions. The corrosion resistance between 723K and 1123K of Ti 6.2.4.6 has also been investigated. There was evidence in favour of parabolic rather than linear increases in weight gain with time and the activation energy associated with parabolic oxidation was estimated at 216KJ/mol. The life of Ti-6246 in argon at 773K was found at certain stresses to be almost twice that obtained in air. This difference could not be explained by the loss of load bearing cross-section area following oxidation. Biaxial creep tests were also carried out at an effective stress of 800 MPa to determine the part taken by the stress state on damage and fracture in the 6.2.4.6 alloy.
17
Girdwood, R. B. "Creep and creep recovery of the nickel-base superalloy Nimonic 105." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637059.
Texte intégralRésumé :
Uniaxial constant stress creep tests have been performed on the wrought nickel-base superalloy Nimonic 105 at 1098, 1123, 1148, 1173 and 1198K over the stress range 50-450MPa. Entire creep curves were recorded and creep curve shapes analysed. Rejuvenative procedures were applied to pre-crept samples and creep recovery quantitatively assessed.
18
Hull, R. J. "Creep and creep fracture of the near-alpha titanium alloy IMI834." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637341.
Texte intégralRésumé :
High precision uniaxial constant stress tests were carried out for the near-alpha titanium alloy IMI834. Testing was completed at 823, 848, 873, 898 and 923 K, and at stresses chosen to give rupture lives in the range of about one day to six months at each temperature. Over the entire range of testing conditions, predominantly tertiary normal creep curves were recorded. During creep an alpha-case developed at air exposed surfaces, whose depth varied according to a parabolic rate law with an activation energy of 208 kJmol<SUP>-1</SUP>. For tests failing after about 1000 hours at 848, 873 and 898 K, and 100 hours at 923 K, failure occurred due to the propagation of circumferential surface cracks which developed in the alpha-case. In contrast, for all tests at 823 K, and for rupture lives of less than 100 hours at 923 K, and for tests lasting less than about 1000 hours at the remaining temperatures, failure occurred due to the link up of creep cavities formed predominantly at the alpha/transformed beta interfaces. A conventional power law analysis of the creep data proved capable of describing the stress and temperature variation of the minimum creep rates and rupture lives. However, this approach gave no information concerning the evolution of creep strain with time. Consequently, the theta-projection concept and the continuum damage mechanics (CDM) constitutive equations were also fitted to the experimental data. Isothermal and anisothermal forms of each model were developed. These proved capable of representing the stress and temperature variation of the experimental failure times, minimum creep rates and failure strains. However, whilst the theta-projection method described entire creep curves, the creep curves constructed using CDM contained almost no primary stage.
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Stewart, Calvin. "A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6023.
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In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative “damage state” within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creep-fatigue tests are obtained from literature for 304 stainless steel at 600°C (1112°F) in an air. Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN one-dimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.<br>Ph.D.<br>Doctorate<br>Mechanical and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering
20
Lieu, T. D. "Creep and creep fracture of MA 957 oxide dispersion-strengthened ferritic steel." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637910.
Texte intégralRésumé :
The creep and creep fatigue properties of a 14% Cr ferritic steel (MA 957) strengthened with a dispersion of Y<SUB>2</SUB>O<SUB>3</SUB> particles have been determined using high precision constant stress creep machines. Creep testing was carried out under tension over a stress range of 250 to 420 MPa at 873 to 973K. In addition, compression creep tests were also performed over a stress range of 250 to 320 MPa at 948K. Normal creep curves were observed under all tensile conditions, i.e. after the initial strain on loading, the strain rate decreased to an apparently steady state before the onset of a tertiary stage leading to fracture. Curve shapes varied with testing conditions. At low temperatures, all creep curves were primary dominated. At higher temperatures, the creep curve shapes were primary dominated at low stresses but tertiary dominated at higher stresses. Like all oxide dispersion-strengthened alloys (ODS), the stress exponent (<I>n</I>) and the activation energy (<I>Q</I><SUB>c</SUB>) values of MA 957 were found to be anomalously large; <I>n</I> varied from 25 to 52, whilst <I>Q</I><SUB>c</SUB> varied from 498 to 856 KJmol<SUP>-1</SUP> over the stress and temperature ranges studied. Despite much research on ODS alloys, power law creep behaviour of ODS alloys is still not well understood. Thus, the creep properties of MA 957 were analysed using the θ methodology. It was shown that entire creep curves can be constructed accurately when using the θ Projection Concept, allowing minimum creep rates and times to failure to be calculated for any stress and temperature. Moreover, this study indicated that the complex behaviour patterns observed when power law equations are used to describe the creep properties of MA 957 can be rationalised convincingly using the θ methodology.
21
Havel, Frantisek. "Creep in soft Soils." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-297.
Texte intégralRésumé :
<p>As more and more constructions are concentrated in densely populated urban areas, there is an increasing need to construct buildings and geotechnical structures on soft clay materials, which usually produce significant creep deformation. Although a lot of research work has been related to the creep behaviour of a natural clay material, there are still many questions about this phenomenon. Even today, prediction of the time dependent deformation is generally very problematic. Detailed laboratory, in-situ and numerical studies of soft soil creep are necessary for the better understanding and consequently, better prognosis of this behaviour. All these studies were performed and will be presented in this thesis.</p><p>The long-term, one-dimensional consolidation has been investigated by oedometer tests on undisturbed Norwegian Kvenild quick clay, undisturbed Norwegian Glava clay, undisturbed and remolded Norwegian Onsøy clay and undisturbed Czech Terlicko clayey shale. All tests have been performed in an incremental loading oedometer apparatus with a lever arm, where, in the case of the Glava clay and the Terlicko clayey shale, two sizes of oedometer rings have been used. Detailed means of evaluating the stress-strain-time oedometer behaviour using a time resistance concept introduced by Professor Nilmar Janbu [46,48] is described. The application of the Soft-soil-creep model is presented. This is implemented in the geotechnical finite element program PLAXIS 8.1, for the mathematical modelling of the longterm oedometer test, with emphasis on the correct choice of the input parameters based on the oedometer test results, and their influence to the model’s behaviour.</p><p>The undrained and drained deviatoric creep behaviour of the Norwegian Glava clay and the Czech Terlicko clayey shale have been studied under triaxial compression. Two different triaxial apparatuses have been used in the study - standard triaxial apparatus made by Wille Geotechnik Gmbh and unique Creep Triaxial apparatus made at NTNU. A large number of undrained and drained deviatoric creep tests under different conditions have been carried out on 100x50 mm (1:2) and 50x50 mm (1:1) cylindrical specimens. Evaluation of the deviatoric creep behaviour based on the time resistance concept together with detailed description of tests conditions is reported. Data is presented showing the relation between stress level, i.e. degree of shear mobilisation at the start of the creep, time, pore pressure development and accumulated axial creep strain. Significant effort has been put into the study of the undrained triaxial tests on 1:1 clay specimens in general and undrained deviatoric creep triaxial tests on 1:1 clay specimens in particular. The problem connected with the pore pressure development and measurement is presented. A 2D numerical study of the undrained triaxial deviatoric creep tests has been done on 1:1 and 1:2 specimens using the finite element program PLAXIS 8.1. There is also a comparison of the laboratory and numerical behaviour.</p><p>Study of the viscosity and creep behaviour of a natural clay has been performed with modular compact rheometer. The MCR 300 rheometer has been used for the rheological investigation of the Norwegian Glava clay. Oscillatory, rotational and creep tests have been done with this apparatus. The basic characterisation of these tests is presented together with their evaluation. Deviatoric creep tests on modular compact rheometer have been evaluated based on the time resistance concept and compared with deviatoric creep tests on a standard triaxial apparatus. The analysis of the Czech Terlicko dam with emphasis on the creep behaviour has been performed based on the cooperation with the Povodi Odry, a.s., Czech Republic. A detailed investigation of the undisturbed clayey shale from the Terlicko dam substratum has been done in the geotechnical and geological laboratory. The characterisation of Terlicko clayey shale is reported base on the laboratory tests results. The in-situ behaviour of the Terlicko dam with emphasis to the uplift of the righthand slope hillside is described. In order to understand the in-situ behaviour a numerical study of the Terlicko dam has been done with PLAXIS 8.1 and Soft-soilcreep model. Results from this 2D numerical test together with recommendations and suggestions are presented.</p>
22
Feng, Gang, and 封剛. "Creep effects in nanoindentation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31224350.
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Resen, Abdul-Amir S. "Biaxial creep of plastics." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256753.
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Liu, Qida. "Electromechanical creep in ferroelectrics." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613330.
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Feng, Gang. "Creep effects in nanoindentation." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23273288.
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Yu, Chi-Wen. "Creep characteristics of soft rock and modelling of creep in tunnel : determination of creep characteristics of soft rock and development of non-linear creep analysis code for squeezing tunnel problem." Thesis, University of Bradford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.586717.
Texte intégralRésumé :
Squeezing or time-dependent creep deformation of rock has been encountered frequently in tunnels. It is particularly common in tunnels excavated in very soft rock or heavily fractured rock under significant in-situ stresses. In Taiwan, due to the inferior geological setting and the young sedimentary rock formations, squeezing in tunnels was found to be a very common problem from the recent case histories of some large span road tunnels. This research reviewed the existing rock creep models, and an adequate creep model for representing the creep behaviour of soft rock or a weak rock mass in general was selected based on testing data of some soft rock cores. A numerical code was developed and validated by using tunnel physical model test. Actual tunnel case histories were also used to develop the creep analysis method for practical engineering purpose.
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DeMaio, Andrew Marc. "The Role of Bonding on the Tensile Creep Behavior of Paper." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/16329.
Texte intégralRésumé :
The role of bonding in the tensile creep behavior of paper was analyzed. This was accomplished by producing handsheets at a range of different bonding levels through manipulation of relative bonded area and specific bond strength. This was done by varying the level of wet pressing (to change relative bonded area) and using debonding and bonding agents (to change specific bond strength). Once manufactured, sheets underwent an extensive battery of physical testing and creep testing. Creep testing was conducted under constant humidity and cyclic humidity (accelerated creep) conditions. Microscopic analysis techniques were also employed to visually study bonded area loss from creep strain. Two mathematical models (one empirical and one rheological) were created to isolate, account for, and incorporate bonding into predicting tensile creep behavior in paper. Overall, the results from this thesis show that the role of bonding in tensile creep behavior (and accelerated creep behavior) is no different than its role in stress-strain behavior, which is a new finding. This means the bonding influence on tensile creep behavior is related to sheet efficiency and how effectively stress is distributed within the structure, bonded area loss is a strain-induced phenomenon and bonding is not the cause of accelerated creep behavior.
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Palmer, C. J. "High temperature creep of copper." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638403.
Texte intégralRésumé :
The key observations that have underpinned traditional power law approaches to creep mechanism identification have been re-evaluated using information obtained for pure copper and aluminium, and also for various other metals and alloys. Specifically, data is presented which show stress/creep rate plots for copper and aluminium over extended stress ranges to be well represented by continuous curves, contradicting the common assumption that a transition in mechanisms occurs as the stress is reduced. Data is also presented from a series of stress interruption tests on pure copper, with strain/strain rate responses which also suggest that essentially the same mechanism dominates creep behaviour at high and low stresses. Furthermore, results for copper single crystals and polycrystals are shown which contradict the assumption that dislocation creep processes are grain size independent so the creep rate increases rapidly with decreasing grain diameter only when diffusional mechanisms are dominant at low stresses. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing stress conditions. The superior predictive capabilities of curve shape analysis are then illustrated by results showing accurate predictions of creep behaviour in the low stress region may be obtained from data generated experimentally at far high stresses. Finally, results are presented showing the effects of a range of room temperature prestrains which illustrate the importance of distinguishing between the contributions made by the grain interiors and the grain boundary zones to the overall rates of strain accumulation during creep.
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Wang, D. "Creep of 316 stainless steel." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639338.
Texte intégralRésumé :
Constant stress creep tests were carried out for 316 stainless steel at 550, 600, 650 and 700<SUP>o</SUP>C over the stress range of 125 - 500 MPa. Entire creep curves were recorded by computer and creep curve shapes analysed. Within the stress and temperature range of the test matrix, creep curve shapes vary from tertiary dominant at low stress and temperature, to primary dominant at high temperature and mixed type at intermediate temperatures. Traditional parametric methods such as Larson-Miller, Orr-Dorn-Sherby and Manson-Succop methods were applied for the analysis of creep rupture life. The extrapolative capabilities of these parameters are limited because of the uncertainties involved in the estimation of constants, and the variation of these parameters with stress does not show a smooth 'master curve'. In order to model the entire creep curve rather than just a few creep properties, three different constitutive equations, i.e. equations from Continuum Damage Mechanics (CDM), equations proposed by researchers in National Physical Laboratory in development of Crispen mode, and the θ projection concept, were applied for the analysis of experimental data. Predictions by each approach were also compared with independent data from National Engineering Laboratory. Computer programmes were written for the estimation of constants involved in the CDM equations. No systematic trend was found in the variation of these constants with temperature. Therefore extrapolation of creep data by CDM approach can only be carried out on an isothermal basis. For the implementation of Crispen model, a new procedure for the estimation of equation constants was proposed. Using this procedure, the constants obtained were shown to vary systematically with stress and temperature, in a manner similar to the variation of the θ parameters with test conditions. The θ projection concept can accurately describe creep curve shapes and their variation with stress and temperature. Predictions of any creep properties can thus be made from short term test data to long duration.
30
Sun, Wei. "Creep of service-aged welds." Thesis, University of Nottingham, 1996. http://eprints.nottingham.ac.uk/11727/.
Texte intégralRésumé :
The creep behaviour of welds in service-aged pipes are studied. The aims of the research have been achieved using analytical, numerical and experimental approaches to the relevant subjects. Several features of the work are presented: (i) a systematic parametric study of the creep of two-material test specimens including a stress singularity analysis, (ii) an impression creep testing method using a rectangular indenter, which can be applied to study the creep properties in welds, and (iii) methods used for damage constitutive equation generation involving FE-damage modelling of the rupture tests of cross-weld specimens. General observations on the creep of two-material structures have been made using analytical solutions derived from four simple structures. The effects of geometries and relative creep properties on the creep stress or strain-rate distributions have been investigated using the finite element approach with idealised, two-material, axisymmetric models. The stress variations have been extensively studied on the centre-line and in the singularity regions of the models. An impression creep testing technique with a "long" rectangular indenter has been developed for the study of the creep properties in the narrow zones within weldments. The effect of varying the geometric test parameters has been fully analysed. The application and the possible advantages of the technique for determining the creep properties in welded components have been highlighted. Experimental testing has been performed for the purpose of verifying the impression creep testing technique and to provide the creep and rupture information required for the generation of creep and damage parameters for the exposed materials. The results obtained have further validated the applicability of the impression creep testing technique. Creep continuum damage investigations have been performed in order to generate the material parameters in a continuum damage constitutive equation and to model practical weldments. The methods used for material data generation have been established. The failure analysis and prediction for the service-aged welded pipes using steady-state analysis, damage modelling and extrapolation technique have been addressed.
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Rayner, Glen. "Creep of welded branched pipes." Thesis, University of Nottingham, 2004. http://eprints.nottingham.ac.uk/11660/.
Texte intégralRésumé :
Creep failure of welds in high-temperature power plant steam piping systems is known to be a potential cause of plant failure. Creep behaviour of plain pipes with circumferential welds and cross-weld specimens have received fairly extensive attention. However, research into the creep behaviour of welded thick-walled branched steam pipes has received less attention. Consequently, this thesis addresses improving the understanding of the creep behaviour for this type of geometry. Numerical and analytical methods are used to assess the creep behaviour of typical power plant branched pipe geometries. The effects of various geometric and material parameters on the creep stress and creep life behaviour of the connections are studied. In particular, the effect of the differing creep properties associated with the various material regions of the weld are investigated. The importance of incorporation of weld properties in creep life assessments is thus assessed. Finite element steady-state and continuum damage mechanics creep analyses have been used to identify the relative creep strength of typical connections compared to plain pipes. The work identifies typical creep rupture locations within branched pipe welds and the associated damage accumulation at and around these positions. Various creep life assessment methods/procedures are used in practise: these are mainly the British Standard codes, British Energy's R5 procedure, steady state creep approaches and continuum damage mechanics approaches. The relative accuracy and conservatism of these distinct approaches are addressed for the application to typical branched pipes. The general formulation of steady-state creep stress is applied to the parametric study of weld materials in a typical multi-material welded branched pipe. An approximate interpolation technique for power-law creep is implemented to reduce the number of analyses needed to span a wide range of material parameters. The method is used to estimate the creep stresses and lives at several critical regions within the various material zones of the weld. The advantages of the technique are related to the small number of analyses required and the simple and compact way of presenting the results for weld design and life assessment purposes.
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Ling, Paul Keh Yiing. "Creep of metal matrix composites." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240496.
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Kwok, Chung Yee. "Micromechanical modelling of soil creep." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611185.
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De, Voy Julian David James. "Failure of creep brittle materials." Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/34757.
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Maraboli, Contardo Luis Robinson. "Creep de aleaciones cobre molibdeno." Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/132918.
Texte intégralRésumé :
Ingeniero Civil Mecánico<br>Esta memoria consiste en una investigación en la cual se busca mejorar las propiedades mecánicas del cobre, incorporando una dispersión nanométrica de cerámicos in-situ, mediante molienda reactiva, los cuales dificultan el movimiento de dislocaciones y límites de grano.
Este trabajo tiene por objetivo fabricar aleaciones con dispersión de carburos de molibdeno (específicamente Cu - 0%v Mo2C, Cu - 2,5%v Mo2C y Cu - 5%v Mo2C) y determinar cómo afecta esta composición en la compresión en caliente y creep.
Se realizaron moliendas reactivas de 100 y 150 horas, a partir de polvos elementales de Cu y Mo. Proceso realizado en un molino atritor con bolas de acero y hexano como liquido de molienda. Luego se consolidan los polvos en caliente, a una temperatura de 750ºC. Para cada una de las aleaciones se realizó ensayos de compresión en frio, a una velocidad de 0,5 mm/min, ensayos de compresión en caliente a 500 ºC y 700 ºC, por ultimo ensayos de creep a 50%, 65% y 80% del límite de fluencia.
La caracterización de las aleaciones y polvos fue a través de difracción de rayos x, análisis químico de polvos y microscopia electrónica.
Se estableció que efectivamente a un mayor porcentaje de Mo, el material mejora sus propiedades mecánicas, dando como resultados mayores límites de fluencia y menores velocidades de deformación en caliente, lo cual valida la tesis de la formación de precipitados.
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Couto, Marcelo Guerino Pereira. "'Creep' em resinas compostas fotopolimerizáveis." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/25/25131/tde-11032005-110757/.
Texte intégralRésumé :
As resinas compostas vêm sofrendo inúmeras alterações com o objetivo de tornar o seu uso adequado para restaurações de dentes posteriores, entretanto, problemas clínicos associados à sua utilização são comumente observados, dentre eles sua resistência ao desgaste e à abrasão, a contração de polimerização, a microinfiltrção marginal, e sua deformação permanente (importante propriedade em situações clínicas onde existem áreas sujeitas às forças oclusais) e esta, normalmente não é considerada. Visando determinar o creep, por meio da deformação permanente, amostras confeccionadas com resinas compostas fotopolimerizáveis: ALERT [A] (Jeneric®/Pentron®), CHARISMA F [C] (Heraeus/Kulzer), HELIOMOLAR RADIOPAQUE [H] (Vivadent), SOLITAIRE [S] (Heraeus/Kulzer) e TETRIC CERAM [T] (Vivadent) após armazenamento em água, à temperatura de 37 + 1ºC, foram submetidas a uma carga compressiva constante de 36MPa, por períodos de: 15 minutos, 1 hora e 24 horas. Os resultados obtidos apresentam os valores quantitativos da diferença entre o comprimento original da amostra e o seu comprimento após o ensaio, em cada período estabelecido. A análise estatística dos dados apresentados pelas cinco resinas compostas avaliadas nos quatro períodos determinados, demonstrou resultados de creep estático (em ordem decrescente), para o período de 15 minutos: [H] (X=1,0192%), [T] (X=0,8787%), [C] (X=0,7469%), [S] (X=0,6738%) e [A] (X = 0,5095%). Para o período de 1 hora: [H] (X=1,5546%), [T] (X=1,2082%), [C] (X=0,9744%), [S] (X=0,8245%), [A] (X=0,6348%) e, para o último período observado, 24 horas, obteve-se a seguinte seqüência: [H] (X=2,3747%), [T] (X=1,7993%), [C] (X=1,2812%), [S] (X=1,2645%) e [A] (X=0,7600). Os valores médios do creep estático das resinas CHARISMA F e SOLITAIRE não foram estatisticamente diferentes em qualquer um dos períodos estudados, sendo que no período de 15 minutos, os resultados obtidos para a resina TETRIC CERAM também se assemelharam aos destas e, em 1 hora, os da resina composta ALERT foram similares aos das duas primeiras; porém, a resina HELIOMOLAR RADIOPAQUE, apresentou mensurações divergentes das anteriores, demonstrando piores características de deformação permanente, por possuir maiores valores de creep estático em qualquer período estudado.<br>The posterior composite resins dental restorative materials, have been, extensively, used in substitution of dental amalgam, in function of its aesthetic best. Although the use of those resins, in areas subject to the forces occlusal, increased significantly, the nead evaluation of the behavior of static creepimportant property to be considered in those situationsit is not very disclosed. For this reason, the objective of the present paper was to determine the static creep of the composite resins: Alert [A], Charisma F [C], Heliomolar Radiopaque [H], Solitaire [S] and Tetric Ceram [T], by evaluation means of the permanent deformation. That deformation was determined in specimens submitted to a constant compressive load of 36MPa, in 37 + 1ºC, immerged in recipient contend water, for periods of 15 minutes, 1 hour and 24 hours. The results obtained in that experiment present the quantitative values of the creep in crescent order, for the period of 15 minutes: H, T, C, S, A; in 1 hour: H, T, C, S, A and in 24 hours: H, T, C, S, A. The profile analysis of the creep for five composite resins evaluated in the four pre-determined periods demonstrated similar results for C, S, T in 15 minutes, A, C, S, in 1 hour and C, S for 24 hour, and different for H in every observed time.
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Sieburg, H. O. "Creep predictions for turbomachinery components." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/18697.
Texte intégralRésumé :
Several theories of creep and creep rupture are reviewed. Specific attention is devoted to the brittle damage theory proposed by Kachanov. Creep, damage and life predictions for rectangular or circular cross section beams under bending and tensile loads are presented. Comparison with data for a Ni Superalloy showed life predictions could be 30X in excess of experimental values. This beam model also revealed that it is imperative that no bending moments be inadvertently applied during tensile creep testing. The creep-damage material model is extended to multidimensional situations. A refinement, whereby no damage accumulates in compression, is incorporated. A User-Material subroutine for this constitutive model has been formulated, and incorporated into the ABAQUS FEM package. Several verification examples are presented; one example is the creep-damage behaviour of a notched bar in tension. The value of reference stress techniques is discussed. Reference stress estimates for a centrifugally loaded bar, as well as for a cantilever under distributed loads, are presented. These could be useful in turbine blade design. Bibliography: pages 91-92.
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Neuhofer, Erik Joachim, and af Rolén Samuel Zelenka. "The Feature Creep Perception in Game Development : Exploring the role of feature creep in development methods and employee engagement." Thesis, Södertörns högskola, Medieteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:sh:diva-44946.
Texte intégralRésumé :
Game developers often find themselves coming up with ideas along the production period of a game varying in size and may go unnoticed or seem insignificant to the scope of the project but in the long run add up to break deadlines, budget and affect the morale and engagement of developers. In the modern game development industry agile development methods have increased in popularity allowing flexibility in the development process. This agile approach has emerged from traditional software development where waterfall development methods are common practice (Kanode and Haddad, 2009). Through in-depth interviews with developers from Sweden, Finland, and the United Kingdom this study aims to explore how feature creep is perceived by the individual developer and its effect on the day-to-day development. The ambition is to establish whether feature creeping as a phenomenon can be a useful tool for innovation and work culture.<br>Spelutvecklare får kontinuerligt idéer under produktionen som varierar i storlek och kan gå obemärkta eller anses meningslösa för projektets ramar och över tid och kan påverka deadline, budget, moral och engagemang hos spelutvecklare. I dagens spelindustri har agila arbetsmetoder ökat i popularitet som möjliggör flexibla utvecklingsprocesser. De agila arbetssättet har vuxit fram ur traditionell mjukvaruutveckling där vattenfallsmetoder är ofta förekommit (Kanode och Haddad, 2009). Genom ingående intervjuer med utvecklare från Sverige, Finland och Storbritannien undersöker den här studien hur feature creep upplevs av den enskilda spelutvecklaren och dess effekt på det dagliga utvecklandet i spelbranschen med en ambition att se hur fenomenet feature creep kan vara ett användbart verktyg för innovation och arbetskulturen.
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Larsson, Jonas. "Evaluation of current methods for creep analysis and impression creep testing of power plant steels." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104603.
Texte intégralRésumé :
Destructive testing of creep exposed components is a powerful tool for evaluation of remaining lifetime of high temperature pipe systems. The most common destructive evaluation method used today is uniaxial creep testing. Uniaxial creep tests can produce accurate creep curves but the test method has some drawbacks such as costliness and long testing times. It also demands large sample material outtake which often involve weld repair. Impression creep (IC) testing is a relatively new alternative test method for evaluating primary and secondary creep rates. The scope of this work is to evaluate the benefits and drawbacks of IC testing over uniaxial creep testing in order to determine its usefulness as a test method. A literature survey was carried out over the area creep testing of high temperature pipe systems, with particular focus on impression creep testing. The result of the literature survey clearly showed several benefits with impression creep testing. An IC test series was performed in order to determine the secondary creep rate of a service exposed 10CrMo9-10 high temperature pipe steel. The IC tests were performed by VTT in Finland, using the same test parameter and sample material as in previous projects where the creep properties of the test material were determined by uniaxial creep testing. The result of the predicted secondary creep rate obtained from the IC tests was compared with the secondary creep rates measured during the uniaxial tests. The IC tests results did not align satisfactory with the results from the uniaxial creep tests, which would have been expected. The reason for this may be due to sources of error during impression creep testing, since very small displacements due to creep have to be measured with high precision during the tests. Further testing of the impression creep test method is recommended as a result of this work, in order to evaluate the method.<br>Förstörande provning av krypexponerade komponenter är ett kraftfullt redskap för utvärdering av återstående livslängd hos rörsystem med höga drifttemperaturer. Den vanligaste formen av förstörande provning i dessa fall är idag enaxlig krypprovning. Enaxliga krypprovningar producerar fullständiga krypkurvor men provningsmetoden har vissa nackdelar såsom att den är relativt dyr och tar förhållandevislång tid. Impression creep eller (IC) –provning är en relativt ny, alternativ, testmetod för att utvärdera primär och sekundärkryp. Det här arbetet ämnar utreda för- och nackdelar med IC-provning gentemot enaxlig krypprovning, samt undersöka dugligheten av IC-provning som testmetod. En litteraturstudie över området provning av krypegenskaper hos rörsystem med höga drifttemperaturer, med extra fokus på IC-provning har genomförts. Resultatet av litteraturstudien pekade tydligt på fördelarna med IC provning. En serie IC-tester utfördes också i syfte att bestämma den sekundära kryphastigheten hos ett driftpåkänt 10CrMo9-10 låglegerat tryckkärlsstål avsett för höga drifttemperaturer. IC-provningen gjordes av VTT Finland. Samma testparametrar och samma provmaterial som hade använts i tidigare projekt där krypegenskaperna hos provmaterialet har utvärderats bl.a. genom enaxlig krypprovning. Resultaten från IC-provningen jämfördes med de sekundära krypningshastigheterna som hade observerats vid den enaxliga krypprovningen. Resultaten från IC-provningen visade sig avvika från resultateten från den enaxliga krypprovningen. Orsaken till det kunde inte förklaras. Mätningar av mycket små förskjutningar samt små temperaturavvikelser föreslogs eventuellt kunna leda till felkällor. Som ett resultat av det här arbetet förslås fortsatt utvärdering och provning med IC-metoden behövs innan provningsmetoden kan tas i bruk.
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Stracey, Muhammad Ghalib. "Continuum Damage Mechanics (CDM) modelling of dislocation creep in 9-12% Cr creep resistant steels." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22994.
Texte intégralRésumé :
The generation of electricity to meet an ever-growing demand has become a defining characteristic of the modern world for both developed and developing nations alike. This, coupled with the intensifying concern with pollution and its effects on the environment has put immense pressure on how quickly and efficiently power is produced. Being the most prevalent source of electricity generation, coal fired power plants have been subject to increasing scrutiny and study in an effort to improve the efficiency at which they operate. Hence, coal fired power plants are being run at increased temperatures and pressures such as those observed in Super-critical and Ultra-super-critical plants. This has by extension put excessive demand on materials used in these plants specifically within the boiler and superheater pipe sections where the most extreme thermodynamic conditions are experienced. The most commonly used materials for these applications are in the family of ferritic/martensitic 9-12% Cr steels chosen for their superior material properties especially during long-term exposure as coal fired power plants typically operate for over 20 years before being decommissioned. One of the lesser understood aspects of 9-12%Cr steels is with regard to their long-term material properties specifically that of creep degradation and deformation. This has been partially due to the reliance of creep life predictions in the past being based on accelerated creep testing and empirically based modelling. With the relatively recent revelations of empirically based modelling shown to be inaccurate when extrapolated to the long-term, a need has been identified amongst researchers to develop more accurate models based on physical relationships and material microstructure. Moreover, the insight obtained from modern experimental techniques and technologies as well as ever-expanding computing capabilities provide an opportunity to produce microstructurally based models with a high degree of complexity. Thus motivated, the focus of this dissertation was to develop a physically based dislocation creep model using the Continuum Damage Mechanics (CDM) approach. A dislocation CDM model was developed and implemented in the current work for uniaxial creep loading using the numerical modelling software Matlabᵀᴹ. The CDM approach was built upon fundamental dislocation theory as well as other microstructural considerations pertaining to dislocation creep including subgrain coarsening, M₂₃C₆ precipitate coarsening and stress redistribution. The CDM model was found to require calibration in order to be applied to specific 9- 12% Cr steels which was implemented using a parameter optimisation routine. The results obtained were compared with experimentally obtained, long-term creep-time and microstructural data for the 11% Cr steel CB8 and the 9% Cr steel P92. The CDM creep-time predictions were found to vary in accuracy depending upon the experimental data against which the model was calibrated. Upon further investigation, it was hypothesised that the discrepancy observed was due to the formation of the Modified Z-phase in some of the long term creep data but not in others which was based primarily on the differing creep exposure times of the various samples. The CDM creep-time predictions for P92 were found to be accurate when compared with experimental results regardless of creep exposure times. The apparent difference in the approximation of the creep deformation for the two steels was concluded as being due to the formation of the Modified Z-phase in CB8 but not in P92 as Modified Zphase formation is intrinsically linked with the Cr content of the steel.
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Chang, Yeou Shin. "The effect of the interphase/interface region on creep and creep rupture of thermoplastic composites." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-170854/.
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Chakravarty, Sanjay. "DEVELOPMENT OF CREEP TESTER AND TO INVESTIGATE THE EFFECT OF CATIONIC STARCH ON TENSILE CREEP ON SOFTWOOD BLEACHED KRAFT HANDSHEETS AT CONSTANT HUMIDITY." Miami University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=miami1143250391.
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Zhang, Ruomeng. "Evaluation of Current Concrete Creep Prediction Models." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1461963600.
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Saber, Mohammed. "Experimental and finite element studies of creep and creep crack growth in P91 and P92 weldments." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12197/.
Texte intégralRésumé :
P91 and P92 steels are two ASTM grades of steel which have been used in high temperature applications, such as fossil-fuelled power stations, nuclear power stations and chemical plants. Operating under creep conditions, i.e. high temperature and/or high stress, the welds made from these steels are potential failure locations and, therefore, life limiting for the entire plant. In this thesis, the results of creep and creep crack growth (CCG) tests, which were carried out on P91 and P92 welds, are reported. These tests were carried out on welds constituents, i.e. parent materials (PM) and weld metal (WM), and across-welds, for the P91 material at 650°C and for the P92 material at 675°C. For the cross-weld tests, interest was focused on the Type IV region, a narrow zone at one end of the heat affected zone (HAZ) at the side of the PM. Also reported, in this thesis, are the results of the Finite Element analyses for predicting the creep and creep crack growth in the P91 and P92 materials. For the P91 material, CCG tests were carried out on PM and cross-weld CT specimens, at 650°C. The results of the CCG tests for P91 show that the CCG rates for the cross-weld CT specimens are about ten times higher than those for the PM specimens. For P92, uniaxial and notched bar creep tests were carried out on the PM and WM, at 675°C. Cross-weld uniaxial, notched bar and waisted specimens were also tested in order to characterise the creep behaviour of the P92 HAZ material. Impression creep tests were also carried out on the P92 HAZ material. The results of the CCG tests for P92 show that the CCG rates for the cross-weld CT specimens are about two times higher than these for the PM CT specimens. The fracture mechanics parameter, C*, was used to correlate the CCG rates in the P91 and P92 CT specimens. The load line displacement rates and the CCG data, for the CT specimens, were used to calculate C* values according to ASTM E 1457-00 (2001). The Reference Stress was also found to correlate the CCG rates in the P91 CT specimens. Further, FE analyses were carried out to obtain the values of C*, based on the steady state value of the contour integral C(t). Stationary crack and growing crack CT models were used to obtain the C* values. Damage mechanics theory and equations were used to predict the creep and CCG for the P91 and P92 materials using the commercial FE package, ABAQUS. Both the Kachanov and the Liu and Murakami damage models were used. In order to use these models, material properties have to be determined. The results of creep and creep rupture tests were used to determine those properties. It was found that both damage models could be used to predict the creep behaviour of the tested materials. However, the Liu and Murakami model was favoured over the Kachanov model in predicting the CCG in the CT specimens. The effect of the material multiaxiality is also highlighted.
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Li, Han. "The nanoindentation size effects of creep." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B30696380.
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Segle, Peter. "Numerical simulation of weldment creep response." Doctoral thesis, KTH, Materials Science and Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3359.
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<p>In-service inspections of high temperature pressureequipment show that weldments are prone to creep and fatiguedamage. It is not uncommon that severely damaged weldments arefound even before the design life of the component has beenreached. In order to improve this situation action has beentaken during the last decades, both from industry, universitiesand research institutes, aiming at an enhanced understanding ofthe weldment response.</p><p>The work presented in this thesis focuses on numericalsimulation of weldment creep response. For a more profoundunderstanding of the evolution of creep damage in mismatchedlow alloy weldments, simulations are performed using thecontinuum damage mechanics, CDM, concept. Both design and lifeassessment aspects are addressed. The possibility to assessseam welded pipes using results from tests of cross-weldspecimens taken out from the seam is investigated. It is foundthat the larger the cross-weld specimen the better thecorrelation. The advantage to use the CDM concept prior to aregular creep analysis is also pointed out. In order to developthe CDM analysis, a modified Kachanov-Rabotnov constitutivemodel is implemented into ABAQUS. Using this model, a secondredistribution of stresses is revealed as the tertiary creepstage is reached in the mismatched weldment.</p><p>Creep crack growth, CCG, in cross-weld compact tension, CT,specimens is investigated numerically where a fracturemechanics concept is developed in two steps. In the first one,the C<sup>*</sup>value and an averaged constraint parameter areused for characterising the fields in the process zone, whilein the second step, the creep deformation rate perpendicular tothe crack plane and a constraint parameter ahead of the cracktip, are used as characterising parameters. The influence oftype and degree of mismatch, location of starter notch as wellas size of CT specimen, is investigated. Results show that notonly the material properties of the weldment constituentcontaining the crack, but also the deformation properties ofthe adjacent constituents, influence the CCG behaviour.Furthermore, the effect of size is influenced by the mismatchof the weldment constituents.</p><p>A circumferentially cracked girth weld with differentmismatch is assessed numerically by use of the fracturemechanics concept developed. The results show that type anddegree of mismatch have a great influence on the CCG behaviourand that C<sup>*</sup>alone cannot characterise crack tip fields.Corresponding R5 assessments are also performed. Comparisonwith the numerical investigation shows that the assumption ofplane stress or plane strain conditions in the R5 analysis isessential for the agreement of the results. Assuming the formerresults in a relatively good agreement for the axial stressdominated cases while for the hoop stress dominated cases, R5predicts higher CCG rates by an order of magnitude.</p><p><b>Keywords:</b>ABAQUS, constraint effect, continuum damagemechanics, creep, creep crack growth, design, design code,finite element method, fracture mechanics, life assessment,mismatch, numerical simulation, weldment</p>
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Magnusson, Hans. "Creep modelling of particle strengthened steels." Doctoral thesis, KTH, Materialteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12235.
Texte intégralRésumé :
Materials used in thermal power plants have to resist creep deformation for time periods up to 30 years. Material evaluation is typically based on creep testing with a maximum duration of a few years. This information is used as input when empirically deriving models for creep. These kinds of models are of limited use when considering service conditions or compositions different from those in the experiments. In order to provide a more general model for creep, the mechanisms that give creep strength have to be identified and fundamentally described. By combining tools for thermodynamic modelling and modern dislocation theory the microstructure evolution during creep can be predicted and used as input in creep rate modelling. The model for creep has been utilised to clarify the influence of aluminium on creep strength as a part of the European COST538 action. The results show how AlN is formed at the expense of MX carbonitrides. The role of heat treatment during welding has been analysed. It has been shown that particles start to dissolve already at 800ºC, which is believed to be the main cause of Type IV cracking in commercial alloys. The creep strength of these steels relies on minor additions of alloying elements. Precipitates such as M23C6 carbides and MX carbonitrides give rise to the main strengthening, and remaining elements produce solid solution hardening. Particle growth, coarsening and dissolution have been evaluated. By considering dislocation climb it is possible to determine particle strengthening at high temperatures and long-term service. Transient creep is predicted by considering different types of dislocations. Through the generation and recovery of dislocation densities an increase in work hardening during primary creep is achieved. The role of substructure is included through the composite model. Cavity nucleation and growth are analysed in order to explain the intergranular fracture and to estimate the ductility.<br>QC20100616
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Olagne, Xavier. "An engineering model for snow creep." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27609.
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Snowcovers on slopes densify and deform continuously throughout the winter. These slow, mainly viscous deformations are known as snow creep and this thesis presents an attempt to model them by idealizing snow as a non-Newtonian fluid, where the bulk and shear viscosities depend upon both stress and density. A three-dimensional constitutive law is developed, based largely on analogy with the flow behavior of ice and soil materials.
The model, primarily intended for engineering applications (design of structures erected in a deep snowpack), is tested for creep pressures on long rigid obstacles. Data recorded on two experimental sites are compared with numerical results obtained by the finite element method. In addition to predicting pressures in good agreement with the ones measured in the field, the constitutive law is flexible enough to accommodate the stiffness variations encountered at different locations and hence presents some improvement over the linear formulation.<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate
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Van, Steenis Karen Anne. "Modelling creep deformation in floating ice." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60509.pdf.
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Magnusson, Hans. "Creep modelling of particle strengthened steels." Licentiate thesis, Stockholm : Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4436.
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